The present invention relates to the treatment of subterranean formations. More particularly, the present invention relates to consolidating agent emulsions that comprise convertible surfactant compositions, and their use in subterranean applications.
Hydrocarbon wells are often located in subterranean formations that contain unconsolidated particulates (e.g., sand, gravel, proppant, fines, etc.) that may migrate out of the subterranean formation with the oil, gas, water, and/or other fluids produced by the wells. The presence of such particulates in produced fluids is undesirable in that the particulates may abrade pumping and other producing equipment and/or reduce the production of desired fluids from the well. Moreover, particulates that have migrated into a well bore (e.g., inside the casing and/or perforations in a cased hole), among other things, may clog portions of the well bore, hindering the production of desired fluids from the well. The term “unconsolidated particulates,” and derivatives thereof, is defined herein to include loose particulates and particulates bonded with insufficient bond strength to withstand the forces created by the production of fluids through the formation. Unconsolidated particulates may comprise, among other things, sand, gravel, fines and/or proppant particulates in the subterranean formation, for example, proppant particulates placed in the subterranean formation in the course of a fracturing or gravel-packing operation. The terms “unconsolidated subterranean formations,” “unconsolidated portions of a subterranean formation,” and derivatives thereof are defined herein to include any formations that contain unconsolidated particulates, as that term is defined herein. “Unconsolidated subterranean formations,” and “unconsolidated portions of a subterranean formation,” as those terms are used herein, include subterranean fractures wherein unconsolidated particulates reside within the open space of the fracture (e.g., forming a proppant pack within the fracture).
One method of controlling particulates in such unconsolidated formations has been to produce fluids from the formations at low flow rates, so that the near well stability of sand bridges and the like may be substantially preserved. The collapse of such sand bridges, however, may nevertheless occur, possibly due to unintentionally high production rates and/or pressure cycling as may occur from repeated shut-ins and start ups of a well. The frequency of pressure cycling is critical to the longevity of the near well formation, especially during the depletion stage of the well when the pore pressure of the formation has already been significantly reduced.
One method used to control particulates in unconsolidated formations involves consolidating unconsolidated particulates into stable, permeable masses by applying a consolidating agent (e.g., a resin or tackifying agent) to the subterranean formation. Consolidating agents may be referred to in the art as aggregating or aggregation agents. Such resin application may be problematic when, for example, an insufficient amount of spacer fluid is used between the application of the resin and the application of the external catalyst. The resin may come into contact with the external catalyst in the well bore itself rather than in the unconsolidated subterranean producing zone. When resin is contacted with an external catalyst, an exothermic reaction occurs that may result in rapid polymerization, potentially damaging the formation by plugging pore channels, halting pumping when the well bore is plugged with solid material, or resulting in a downhole explosion as a result of the heat of polymerization. Uniform placement of curable resin into the formations having long intervals is most desirable. However, formations often comprise a wide range of permeabilities even within a single reservoir located along a well bore. As a result, using these conventional processes to treat long intervals (e.g., over about 20 feet) of unconsolidated regions has often heretofore resulted in non-uniform, limited, and/or inadequate penetration distances of consolidating agents into formations.
Oftentimes to protect the consolidating agent from prematurely reacting in the well bore, the consolidating agent may be placed in the well bore via an emulsion. However, the stability of such emulsions can be problematic. For example, some current water-based emulsion systems do not provide strong enough emulsions to carry the consolidating agent downhole. The result is a premature setting of the consolidating agent in an undesirable location in the well bore. This then presents removal issues. Additionally, the consolidating agent is not used for its intended purpose. Additionally, the surfactants that are often used in such emulsions can present clean-up and residue problems. For instance, certain surfactants used heretofore may have undesirable environmental characteristics and/or may be limited by strict environmental regulations in certain areas of the world. As a result, use of these surfactants in subterranean treatments may result in the potential for the bioaccumulation and/or persistence of such surfactants in the environment, which may create potential dangers for their use, such as adverse effects on shrimp and other aqueous aquatic species.